Film bulk acoustic wave resonator (fbar) having stress-relief

ABSTRACT

An acoustic resonator structure comprises: a substrate having a cavity, which has a plurality of sides; a first electrode disposed over the cavity; a piezoelectric layer disposed over a portion of the first electrode and extending over at least one of the sides; and a second electrode disposed over the piezoelectric layer, an overlap of the first electrode, the piezoelectric layer and the second electrode forming an active area of the FBAR. The active area of the FBAR is completely suspended over the cavity.

BACKGROUND

Acoustic resonators are used as oscillators in various electronicapplications. An acoustic resonator can be characterized generally by aresonant frequency and acoustic coupling coefficient kt². However, dueto a variety of intrinsic and extrinsic influences, the resonantfrequency is not stable.

One source of frequency drift in acoustic resonators is physical stress.Physical stress can be caused, for example, by forces transmitted to theacoustic resonator through adjacent components. As an example, anacoustic resonator can be formed on a substrate of a known material, forexample silicon, and comprising components made from various materials.As the substrate is heated and/or cooled, the substrate may expand orcontract unevenly because the various components have differenttemperature coefficients of expansion. This uneven expansion orcontraction can cause the substrate to change shape in a “potato chip”fashion. As the substrate changes shape, the substrate can transferforces to the acoustic resonator through various intervening components.As these forces are transferred to the acoustic resonator, they willchange the resonant frequency of the acoustic resonator, and candeleteriously impact operation of an electronic device that includes theacoustic resonator.

What is needed, therefore, are techniques for reducing frequency driftdue to physical stresses in acoustic resonator structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments are best understood from the followingdetailed description when read with the accompanying drawing figures. Itis emphasized that the various features are not necessarily drawn toscale. In fact, the dimensions may be arbitrarily increased or decreasedfor clarity of discussion. Wherever applicable and practical, likereference numerals refer to like elements.

FIG. 1A is top view of an FBAR structure according to a representativeembodiment.

FIG. 1B is a cross-sectional view of the FBAR structure of FIG. 1A takenalong the line A-A′ of FIG. 1A.

FIG. 1C is a cross-sectional view of the FBAR structure of FIG. 1A takenalong the line B-B′ of FIG. 1A.

FIG. 2A is top view of an FBAR structure according to a representativeembodiment.

FIG. 2B is a cross-sectional view of the FBAR structure of FIG. 2A takenalong the line A-A′ of FIG. 2A.

FIG. 2C is a cross-sectional view of the FBAR structure of FIG. 2A takenalong the line B-B′ of FIG. 2A.

FIG. 3A is top view of an FBAR structure according to a representativeembodiment.

FIG. 3B is a cross-sectional view of the FBAR structure of FIG. 3A takenalong the line A-A′ of FIG. 3A.

FIG. 3C is a cross-sectional view of the FBAR structure of FIG. 3A takenalong the line B-B′ of FIG. 3A.

FIG. 4A is top view of an FBAR structure according to a representativeembodiment.

FIG. 4B is a cross-sectional view of the FBAR structure of FIG. 4A takenalong the line B-B′ of FIG. 4A.

FIG. 5A is top view of an FBAR structure according to a representativeembodiment.

FIG. 5B is a cross-sectional view of the FBAR structure of FIG. 5A takenalong the line A-A′ of FIG. 5A.

FIG. 5C is a cross-sectional view of the FBAR structure of FIG. 5A takenalong the line B-B′ of FIG. 5A.

FIG. 6A is top view of an FBAR structure according to a representativeembodiment.

FIG. 6B is a cross-sectional view of the FBAR structure of FIG. 6A takenalong the line A-A′ of FIG. 6A.

FIG. 6C is a cross-sectional view of the FBAR structure of FIG. 6A takenalong the line B-B′ of FIG. 6A.

FIG. 7A is a top view of an FBAR structure according to a representativeembodiment.

FIG. 7B is a cross-sectional view of the FBAR structure of FIG. 7A takenalong the line A-A′ of FIG. 7A.

FIG. 7C is a cross-sectional view of the FBAR structure of FIG. 7A takenalong the line B-B′ of FIG. 7A.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description, for purposes of explanation andnot limitation, representative embodiments disclosing specific detailsare set forth in order to provide a thorough understanding of thepresent teachings. However, it will be apparent to one having ordinaryskill in the art having had the benefit of the present disclosure thatother embodiments according to the present teachings that depart fromthe specific details disclosed herein remain within the scope of theappended claims. Moreover, descriptions of well-known apparatuses andmethods may be omitted so as to not obscure the description of theexample embodiments. Such methods and apparatuses are clearly within thescope of the present teachings.

The terminology used herein is for purposes of describing particularembodiments only, and is not intended to be limiting. The defined termsare in addition to the technical and scientific meanings of the definedterms as commonly understood and accepted in the technical field of thepresent teachings. In addition, unless expressly so defined herein,terms are not to be interpreted in an overly idealized fashion. Forexample, the terms “isolation” or “separation” are not to be interpretedto require a complete lack of interaction between the describedfeatures.

As used in the specification and appended claims, the terms ‘a’, ‘an’and ‘the’ include both singular and plural referents, unless the contextclearly dictates otherwise. Thus, for example, ‘a device’ includes onedevice and plural devices.

As used in the specification and appended claims, and in addition totheir ordinary meanings, the terms ‘substantial’ or ‘substantially’ meanto within acceptable limits or degree.

As used in the specification and the appended claims and in addition toits ordinary meaning, the term ‘approximately’ means to within anacceptable limit or amount to one having ordinary skill in the art. Forexample, ‘approximately the same’ means that one of ordinary skill inthe art would consider the items being compared to be the same.

Generally, it is understood that the drawings and the various elementsdepicted therein are not drawn to scale. Further, relative terms, suchas “above,” “below,” “top,” “bottom,” “upper” and “lower” are used todescribe the various elements' relationships to one another, asillustrated in the accompanying drawings. It is understood that theserelative terms are intended to encompass different orientations of thedevice and/or elements in addition to the orientation depicted in thedrawings. For example, if the device were inverted with respect to theview in the drawings, an element described as “above” another element,for example, would now be below that element.

The present teachings relate generally to bulk acoustic wave (BAW)resonator structures with the acoustic stack formed over a cavity. Theseacoustic resonator structures can include various types of acousticresonators, such as, for example, FBARs, zero drift resonators (ZDRs),double bulk acoustic resonators (DBARs), and coupled resonator filters(CRFs). In certain embodiments, the BAW resonator structures can be usedto provide electrical filters (e.g., ladder filters).

Contemplated applications of the BAW resonators of the present teachingsinclude, but are not limited to communication filter applications andMEMs applications. For example, the bulk acoustic wave (BAW) resonatorsof the present teachings may be arranged in a ladder-filter arrangement,such as described in U.S. Pat. No. 5,910,756 to Ella, and U.S. Pat. No.6,262,637 to Bradley, et al., the disclosures of which are specificallyincorporated herein by reference. The electrical filters may be used ina number of applications, such as in duplexers.

Certain details of BAW resonators, including materials and methods offabrication, may be found in one or more of the following commonly ownedU.S. patents, patent applications and patent application Publications:U.S. Pat. No. 6,828,713 to Bradley, et al.; U.S. Pat. No. 6,107,721, toLakin; U.S. Pat. Nos. 5,587,620, 5,873,153, 6,384,697, 6,507,983, 7,275,292, 7,388,454 and 7,629,865 to Ruby, et al.; U.S. Pat. No. 7,280,007 toFeng, et al.; U.S. Patent Application Publication No. 2007/0205850 toJamneala, et al.; U.S. Pat. No. 8,248,185 to Choy, et al.; U.S. PatentApplication Publication No. 2010/0327994 to Choy, et al.; U.S. patentapplication Ser. No. 13/662,460 entitled “Bulk Acoustic Wave ResonatorHaving Piezoelectric Layer with Multiple Dopants” to John Choy, et al.and filed on Oct. 27, 2012; and U.S. patent application Publications20110180391 and 20120177816 to Larson, et al. The respective disclosuresof the above patents, patent application publications and patentapplications are specifically incorporated herein by reference. It isemphasized that the components, materials and method of fabricationdescribed in these patents and patent applications are representativeand other methods of fabrication and materials within the purview of oneof ordinary skill in the art are contemplated.

Representative embodiments described below relate to an FBAR structurecomprising an active area that is suspended over a cavity formed in asubstrate, and that is not in contact with the sides of the cavity. Theactive area of the FBAR is supported in various ways so that forcestransmitted to the substrate produce minimal physical stress on theactive area of the FBAR. In other words, the active area of the FBAR issubstantially mechanically isolated from the substrate to prevent theactive area from being influenced by surrounding forces. In this manner,the amount of frequency drift in the FBAR due to physical stress isreduced compared to known FBARs. Moreover, acoustic wave leakage alongthe sides of the cavity is reduced, which results in reduced energyloss, and an increase in the quality (Q) factor of the FBAR compared tocertain known resonators.

Certain embodiments described below can be used in electronicapplications such as low power radios for wireless applications, GPSdevices, and imaging devices, to name but a few. Some embodiments areparticularly relevant to high accuracy devices requiring resonators withminimal frequency drift. For example, some embodiments can be used todisplace existing technologies such as existing Quartz resonators usedin oscillators and in GPS devices.

FIG. 1A is top view of an FBAR structure 100 according to arepresentative embodiment. The FBAR structure 100 comprises a firstelectrode 101, a piezoelectric layer 102 and a second electrode 103stacked over one another. It is noted that for convenience ofexplanation, the piezoelectric layer 102 is depicted in FIG. 1A as beingtransparent so that certain features of the first electrode 101 can bedescribed. The piezoelectric layer 102 is not transparent. Moreover, anoptional passivation layer, which is described below, may be providedover the uppermost layers of the FBAR structure 100, and is not shown inFIG. 1A to better present the description of the arrangement of thelayers of the FBAR structure 100.

The FBAR structure 100 comprises a cavity 104 formed in a substrate 105.The cavity 104 comprises a plurality of sides 106-110, where often, butnot necessarily, the number of the plurality of sides 106-110 is thesame as the number of sides of the first and second electrodes 101, 103.

In a region 111, the piezoelectric layer 102 is removed or otherwise notformed. As described more fully below, piezoelectric layer 102 disposedover at least a portion of the first electrode 101, and extends frombeyond at least one edge of the first electrode 101 and over at leastone of the plurality of sides 106-110 having the first electrode 101extending thereover.

In a representative embodiment, the substrate 105 comprises silicon (Si)or similar material. Generally, the cavity 104 comprises air, and isformed by a known method. The first electrode 101 and the secondelectrode 103 are comprised of a suitable electrically conductivematerial such as tungsten (W) or molybdenum (Mo). The piezoelectriclayer 102 can comprise, for example, aluminum nitride (AlN), zinc oxide(ZnO), or lead zirconium titanate (PZT). Generally, the piezoelectriclayer 102 comprises a highly-textured c-axis piezoelectric materialwhere the c-axis orientations of the crystals of the piezoelectricmaterial are well-collimated, and as such are parallel with one anotherand perpendicular to the plane of the electrodes (e.g., first and secondelectrodes 101, 103).

Many of the details of the materials contemplated for use as thesubstrate 105, first electrode 101, piezoelectric layer 102 and secondelectrode 103, thicknesses of these materials, and details of themethods of manufacture of the FBAR structure 100 are known and aretailored to a particular application. Many of these details aredescribed, for example, in one or more of the patents, patentapplication publications and patent applications incorporated byreference above. Often, these details are not repeated in order to avoidobscuring the description of the present teachings.

As can be seen in FIG. 1A, the second electrode 103 does not overlap theentirety of either the first electrode 101 or the piezoelectric layer102. Rather, the second electrode 103 overlaps only a portion of thearea of the first electrode 101 and the piezoelectric layer 102.Moreover, in the representative embodiment depicted in FIG. 1A, thesecond electrode 103 of the FBAR structure 100 does not extend over anyof the plurality of sides 106-110 of the cavity 104 formed in thesubstrate 105. As such, the active area of the FBAR structure 100, whichis defined as the area of contacting overlap of the second electrode103, the piezoelectric layer 102, the first electrode 101 and the cavity104, is suspended over the cavity 104. In the suspended active area ofFBAR structure 100, an electrical connection is made to the secondelectrode 103 via a bridge 112 that extends over the piezoelectric layer102 and the first electrode 101 and connects to contact 113 disposedover the substrate 105. Illustratively, the bridge 112 is formedaccording to the teachings of the above-referenced, commonly owned U.S.Pat. No. 8,248,825 to Choy, et al. As depicted in FIG. 1A, a signal feedline (SFL) length is a measure of the distance between the active areaof the FBAR structure 100 and its contact side(s) with the substrate105.

The greater the SFL length, the more remote the active area of the FBARstructure 100 is from its contact side(s) (often referred to as the“anchor side(s)” or “feeding side(s)”) with the substrate 105 and theinfluence of stress induced on the substrate 105. As such, the length ofthe bridge 112 is made large compared to known bridges and signal feedsbetween external contacts to the FBAR structure. Illustratively, the SFLlength is at least 25 μm, and typically can be approximately 10 μm toapproximately 100 μm or more. Other structures, such as a double-bridgearrangement described below, can be implemented to provide a suitableSFL length and thus, beneficial mechanical isolation of the active areaof the FBAR structures of representative embodiments.

By this arrangement, the active area of the FBAR structure 100 issubstantially mechanically isolated from the contact or anchor side onthe substrate 105, and therefore, is not significantly susceptible tomechanical stress from the substrate 105. Beneficially, this substantialisolation of the active area of the FBAR structure 100 from mechanicalstress from the contact side or anchor side(s) with the substrate 105reduces the drift of the resonator frequency of the FBAR structure 100.

FIG. 1B is a cross-sectional view of the FBAR structure 100 of FIG. 1Ataken along the line A-A′ of FIG. 1A. The FBAR structure 100 comprisesthe first electrode 101, the piezoelectric layer 102 and the secondelectrode 103 disposed over the cavity 104 in the substrate 105. In arepresentative embodiment, a passivation layer 114 (not shown in FIG.1A) is disposed over the second electrode 103. The passivation layer 114can be formed of various types of materials, including aluminum nitride,silicon carbide, BSG, SiO₂, SiN, polysilicon, and the like. Thethickness of the passivation layer 114 should generally be sufficient toinsulate the layers of FBAR structure 100 from the environment,including protection from moisture, corrosives, contaminants, anddebris.

As depicted in FIG. 1B, an active area 115 of the FBAR structure 100consists of the contacting overlap of the first electrode 101, thepiezoelectric layer 102, the second electrode 103 and the cavity 104.The active area 115 is substantially suspended over the cavity 104 andis supported by the portion of the first electrode 101 that extends overthe side 106 of the cavity 104. However, the first electrode 101 doesnot extend across side 109 of the cavity 104, and the piezoelectriclayer 102 is removed or otherwise not formed in region 111. As such, theactive area 115 is supported at side 106 of the cavity 104, and issubstantially mechanically isolated from the substrate 105 as a result.

FIG. 1C is a cross-sectional view of the FBAR structure 100 of FIG. 1Ataken along the line B-B′ of FIG. 1A. The FBAR structure 100 comprisesthe first electrode 101, the piezoelectric layer 102 and the secondelectrode 103 disposed over the cavity 104 in the substrate 105. Asdepicted in FIG. 1C, the active area 115 of the FBAR structure 100 issubstantially suspended over the cavity 104 and is supported by theportion of the first electrode 101 that extends over the side 107 of thecavity 104. However, the first electrode 101 does not extend across side110 of the cavity 104, and the piezoelectric layer 102 is removed orotherwise not formed in region 111. As such, the active area 115 issupported at side 107 of the cavity 104, and is substantiallymechanically isolated from the substrate 105 as a result.

As depicted in FIG. 1C, the bridge 112 is physically separated from thepiezoelectric layer 102 by space 116, and as such terminates thecontacting overlap of the first electrode 101, the piezoelectric layer102 and the second electrode 103, and as such terminates the active area115 of the FBAR structure 100. In a representative embodiment, the space116 is empty, comprising only air. In other representative embodiments,the space 116 is filled with a non-conductive dielectric material 117that improves the mechanical strength of the bridge and provides thermalresistance to the substrate 105, which generally comprises silicon.Non-conductive dielectric material 117 may be silicon dioxide, which hasmuch greater thermal resistance than pure silicon, or non-etchableboro-silica glass (NEBSG). Other materials within the purview of one ofordinary skill in the art having the benefit of the present disclosureare also contemplated for use as the non-conductive dielectric material117.

In the presently described representative embodiment, the active area115 of the FBAR structure 100 is supported through the mechanicalconnection of the first electrode 101 to the substrate 105 over sides106 and 107 of the cavity 104, and remains unconnected to the remainingsides 108, 109 and 110 of the cavity 104. It is emphasized that this ismerely illustrative, and the active area 115 may be supported throughthe mechanical connection of the first electrode 101 to the substrate105 on only one of the plurality of sides 106˜110. As should beappreciated by one of ordinary skill in the art, the fewer the number ofsides of the first electrode 101 to the substrate 105, the better themechanical isolation of the active area 115 from the substrate 105. Assuch, in representative embodiments, the first electrode 101 ismechanically connected to the substrate 105 through extension of thefirst electrode 101 over at least one of the plurality of sides 106˜110of the substrate 105, but connections to substrate 105 by the extensionof first electrode 101 over more than two of the plurality of sides106˜110 is generally avoided.

As noted above, and as depicted in FIG. 1B, the piezoelectric layer 102is disposed over at least a portion of the first electrode 101, andextends over at least one of the plurality of sides 106˜110 of thecavity 104 having the first electrode 101 extending thereover. So, forexample, in the presently described embodiment, the piezoelectric layer102 is provided over the first electrode 101 and both the firstelectrode 101 and the piezoelectric layer 102 extend over sides 106 and107 of the substrate 105. The extension of the piezoelectric layer 102over side 106 provides mechanical robustness to the FBAR structure 100,and beneficially reduces the susceptibility of the FBAR structure 100 tomechanical failure or fatigue, especially over time.

FIG. 2A is a top view of an FBAR structure 200 according to arepresentative embodiment. Many details of the FBAR structure 200 aresubstantively the same as those provided in the description of FBARstructure 100. These details are not always repeated in order to avoidobscuring the description of the presently described representativeembodiments.

The FBAR structure 200 comprises a first electrode 201, a piezoelectriclayer 202 and a second electrode 203 stacked over one another. It isnoted that for convenience of explanation, the piezoelectric layer 202is depicted in FIG. 2A as being transparent so that certain features ofthe first electrode 201 can be described. The piezoelectric layer 202 isnot transparent. Moreover, an optional passivation layer, which isdescribed below, may be provided over the uppermost layers of the FBARstructure 200, and is not shown in FIG. 2A to better present thedescription of the arrangement of the layers of the FBAR structure 200.

The FBAR structure 200 comprises a cavity 204 formed in a substrate 205.The cavity 204 comprises a plurality of sides 206˜210, where often, butnot necessarily, the number of the plurality of sides 206˜110 is thesame as the number of sides of the first and second electrodes 201, 203.

In a region 211, the piezoelectric layer 202 is removed or otherwise notformed. As described more fully below, piezoelectric layer 202 disposedover at least a portion of the first electrode 201, and extends frombeyond at least one edge of the first electrode 201 and over at leastone of the plurality of sides 206˜110 having the first electrode 201extending thereover.

As can be seen in FIG. 2A, the second electrode 203 does not overlap theentirety of either the first electrode 201 or the piezoelectric layer202. Rather, the second electrode 203 overlaps only a portion of thearea of the first electrode 201 and the piezoelectric layer 202.Moreover, in the representative embodiment depicted in FIG. 2A, thesecond electrode 203 of the FBAR structure 200 does not extend over anyof the plurality of sides 206˜210 of the cavity 204 formed in thesubstrate 205. As such, the active area of the FBAR structure 200, whichis defined as the area of contacting overlap of the second electrode203, the piezoelectric layer 202, the first electrode 201 and the cavity204, is suspended over the cavity 204. As depicted in FIG. 2A, the SFLlength is comparatively large by the extension of the second electrode203 from side 207. As described more fully below, by this beneficialarrangement, the active area of the FBAR structure 200 is substantiallymechanically isolated from the contact side with the substrate 205, andtherefore, is not susceptible to mechanical stress from the substrate205. Beneficially, this substantial isolation of the active area of theFBAR structure 200 from mechanical stress of the substrate 205 reducesthe drift of the resonant frequency f the FBAR structure 200.

FIG. 2B is a cross-sectional view of the FBAR structure 200 of FIG. 2Ataken along the line A-A′ of FIG. 2A. The FBAR structure 200 comprisesthe first electrode 201, the piezoelectric layer 202 and the secondelectrode 203 disposed over the cavity 204 in the substrate 205. In arepresentative embodiment, a passivation layer 214 (not shown in FIG.2A) is disposed over the second electrode 203. The passivation layer 214can be formed of various types of materials, including aluminum nitride,silicon carbide, BSG, SiO₂, SiN, polysilicon, and the like. Thethickness of the passivation layer 214 should generally be sufficient toinsulate the layers of FBAR structure 200 from the environment,including protection from moisture, corrosives, contaminants, anddebris.

As depicted in FIG. 2B, an active area 215 of the FBAR structure 200consists of the contacting overlap of the first electrode 201, thepiezoelectric layer 202, the second electrode 203 and the cavity 204.The active area 215 is substantially suspended over the cavity 204 andis supported by the portion of the first electrode 201 that extends overthe side 206 of the cavity 204. However, the first electrode 201 doesnot extend across side 209 of the cavity 204, and the piezoelectriclayer 202 is removed or otherwise not formed in region 211. As such, theactive area 215 is supported at side 206 of the cavity 204, and issubstantially mechanically isolated from the substrate 205 as a result.

FIG. 2C is a cross-sectional view of the FBAR structure 200 of FIG. 2Ataken along the line B-B′ of FIG. 2A. The FBAR structure 200 comprisesthe first electrode 201, the piezoelectric layer 202 and the secondelectrode 203 disposed over the cavity 204 in the substrate 205. Asdepicted in FIG. 2C, the active area 215 of the FBAR structure 200 issubstantially suspended over the cavity 204. Notably, the piezoelectriclayer 202 extends over the side 207, with the first electrode 201terminating over the cavity 204 as depicted. However, the firstelectrode 201 does not extend across either side 207 or 210 of thecavity 204, and the piezoelectric layer 202 is removed or otherwise notformed in region 211. As such, the active area 215 is supported at side206 of the cavity 204, and is substantially mechanically isolated fromthe substrate 205 as a result.

In the presently described representative embodiment, the active area215 of the FBAR structure 200 is supported through the mechanicalconnection of the first electrode 201 to the substrate 205 over side 206of the cavity 204, and remains unconnected to the remaining sides 207,208, 209 and 210 of the cavity 204. As such, in the presently describedrepresentative embodiment, the active area 215 is supported through themechanical connection of the first electrode 201 to the substrate 205 ononly one of the plurality of sides 206˜210. As should be appreciated byone of ordinary skill in the art, the fewer the number of sides of thefirst electrode 201 to the substrate 205, the better the mechanicalisolation of the active area 215 from the substrate 205. As such, inrepresentative embodiments, the first electrode 201 is mechanicallyconnected to the substrate 205 through extension of the first electrode201 over at least one of the plurality of sides 206˜210 of the substrate205, but connections to substrate 205 by the extension of firstelectrode 201 over more than two of the plurality of sides 206˜120 isgenerally avoided.

As noted above, and as depicted in FIG. 2B, the piezoelectric layer 202is disposed over at least a portion of the first electrode 201, andextends over at least one of the plurality of sides 206˜210 of thecavity 204 having the first electrode 201 extending thereover. So, forexample, in the presently described embodiment, the piezoelectric layer202 is provided over the first electrode 201 and both the firstelectrode 201 and the piezoelectric layer 202 extend over side 206 ofthe substrate 205. The extension of the piezoelectric layer 202 overside 206 provides mechanical robustness to the FBAR structure 200, andbeneficially reduces the susceptibility of the FBAR structure 200 tomechanical stress from the substrate 205.

FIG. 3A is top view of an FBAR structure 300 according to arepresentative embodiment. Many details of the FBAR structure 300 aresubstantively the same as those provided in the description of FBARstructures 100, 200. These details are not always repeated in order toavoid obscuring the description of the description of the presentlydescribed representative embodiments.

The FBAR structure 300 comprises a first electrode 301, a piezoelectriclayer 302 and a second electrode 303 stacked over one another. It isnoted that for convenience of explanation, the piezoelectric layer 302is depicted in FIG. 3A as being transparent so that certain features ofthe first electrode 301 can be described. The piezoelectric layer 302 isnot transparent.

The FBAR structure 300 comprises a cavity 304 formed in a substrate 305.The cavity comprises a plurality of sides 306˜310, where generally thenumber of the plurality of sides 306˜110 is the same as the number ofsides of the first and second electrodes 301, 303.

In a region 111, the piezoelectric layer 302 is removed or otherwise notformed. As described more fully below, piezoelectric layer 302 disposedover at least a portion of the first electrode 301, and extends frombeyond at least one edge of the first electrode 301 and over at leastone of the plurality of sides 306˜110 having the first electrode 301extending thereover.

As can be seen in FIG. 3A, the second electrode 303 does not overlap theentirety of either the first electrode 301 or the piezoelectric layer302. Rather, the second electrode 303 overlaps only a portion of thearea of the first electrode 301 and the piezoelectric layer 302.Moreover, in the representative embodiment depicted in FIG. 3A, thesecond electrode 303 of the FBAR structure 300 does not extend over anyof the plurality of sides 306˜110 of the cavity 304 formed in thesubstrate 305. As such, the active area of the FBAR structure 300, whichis defined as the area of contacting overlap of the second electrode303, the piezoelectric layer 302, the first electrode 301 and the cavity304, is suspended over the cavity 304. As described more fully below, bythis beneficial arrangement, the active area of the FBAR structure 300is substantially mechanically isolated from the substrate 305, andtherefore, is not susceptible to mechanical stress from the substrate305. Beneficially, this substantial isolation of the active area of theFBAR structure 300 from mechanical stress of the substrate 305 reducesthe drift of the center frequency and bandwidth of the FBAR structure300.

FIG. 3B is a cross-sectional view of the FBAR structure 300 of FIG. 3Ataken along the line A-A′ of FIG. 3A. The FBAR structure 300 comprisesthe first electrode 301, the piezoelectric layer 302 and the secondelectrode 303 disposed over the cavity 304 in the substrate 305. In arepresentative embodiment, a passivation layer 314 (not shown in FIG.3A) is disposed over the second electrode 303. The passivation layer 314can be formed of various types of materials, including aluminum nitride,silicon carbide, BSG, SiO₂, SiN, polysilicon, and the like. Thethickness of the passivation layer 314 should generally be sufficient toinsulate the layers of FBAR structure 300 from the environment,including protection from moisture, corrosives, contaminants, anddebris.

As depicted in FIG. 3B, an active area 315 of the FBAR structure 300consists of the contacting overlap of the first electrode 301, thepiezoelectric layer 302, the second electrode 303 and the cavity 304.The active area 315 is substantially suspended over the cavity 304 andis supported by the portion of the first electrode 301 that extends overthe side 306 of the cavity 304 and over the substrate 305. However, thefirst electrode 301 does not extend across side 309 of the cavity 304,and the piezoelectric layer 302 is removed or otherwise not formed inregion 311. As such, the active area 315 is supported at side 306 of thecavity 304, and is substantially mechanically isolated from thesubstrate 305 as a result. Moreover, and in contrast to FBAR structures100, 200 described in connection with representative embodiments above,the piezoelectric layer 302 is removed or otherwise not formed so as tonot extend over the side 306 of the cavity 304 or over the substrate305. Beneficially, by not extending the piezoelectric layer 302 over theside 306 and over the substrate 305, mechanical isolation of the activearea 315 from the mechanical stresses/forces on the substrate 305 isfurther improved.

FIG. 3C is a cross-sectional view of the FBAR structure 300 of FIG. 3Ataken along the line B-B′ of FIG. 3A. The FBAR structure 300 comprisesthe first electrode 301, the piezoelectric layer 302 and the secondelectrode 303 disposed over the cavity 304 in the substrate 305. Asdepicted in FIG. 3C, the active area 315 of the FBAR structure 300 issubstantially suspended over the cavity 304. Notably, the piezoelectriclayer 302 extends over the side 307, with the first electrode 301terminating over the cavity 304 as depicted. However, the firstelectrode 301 does not extend over either side 307 or 310 of the cavity304 or over the substrate 305, and the piezoelectric layer 302 isremoved or otherwise not formed in region 311. As such, the active area315 is supported by the first electrode 301 only at side 306 of thecavity 304, and is substantially mechanically isolated from thesubstrate 305 as a result.

In the presently described representative embodiment, the active area315 of the FBAR structure 300 is supported through the mechanicalconnection of the first electrode 301 to the substrate 305 over side 306of the cavity 304, and remains unconnected to the remaining sides 307,308, 309 and 310 of the cavity. As such, in the presently describedrepresentative embodiment, the active area 315 is supported through themechanical connection of the first electrode 301 to the substrate 305 ononly one of the plurality of sides 306˜310. As should be appreciated byone of ordinary skill in the art, the fewer the number of sides of thefirst electrode 301 connected to the substrate 305, the better themechanical isolation of the active area 315 from the substrate 305. Assuch, in representative embodiments, the first electrode 301 ismechanically connected to the substrate 305 through extension of thefirst electrode 301 over at least one of the plurality of sides 306˜310of the substrate 305, but connections to substrate 305 by the extensionof first electrode 301 over more than two of the plurality of sides306˜310 is generally avoided.

As noted above, and as depicted in FIG. 3B, the piezoelectric layer 302is disposed over at least a portion of the first electrode 301, andextends over at least one of the plurality of sides 306˜310 of thecavity 304. So, for example, in the presently described representativeembodiment, the piezoelectric layer 302 is provided over the firstelectrode 301, but only the piezoelectric layer 302 extends over side307 of the substrate 305. The extension of the piezoelectric layer 302over side 307 provides mechanical robustness to the FBAR structure 300,and beneficially reduces the susceptibility of the FBAR structure 300 tomechanical failure or fatigue, especially over time.

FIG. 4A is top view of an FBAR structure 400 according to arepresentative embodiment. Many details of the FBAR structure 400 aresubstantively the same as those provided in the description of FBARstructures 100˜300. These details are not always repeated in order toavoid obscuring the description of the presently describedrepresentative embodiments.

The FBAR structure 400 comprises a first electrode 401, a piezoelectriclayer 402 and a second electrode 403 stacked over one another. It isnoted that for convenience of explanation, the piezoelectric layer 402is depicted in FIG. 4A as being transparent so that certain features ofthe first electrode 401 can be described. The piezoelectric layer 402 isnot transparent. Moreover, an optional passivation layer, which isdescribed below, may be provided over the uppermost layers of the FBARstructure 400, and is not shown in FIG. 4A to better present thedescription of the arrangement of the layers of the FBAR structure 400.

The FBAR structure 400 comprises a cavity 404 formed in a substrate 405.The cavity comprises a plurality of sides 406˜410, where generally thenumber of the plurality of sides 406˜410 is the same as the number ofsides of the first and second electrodes 401, 403.

In a region 411, the piezoelectric layer 402 is removed or otherwise notformed. As described more fully below, piezoelectric layer 402 isdisposed over at least a portion of the first electrode 401, and extendsfrom beyond at least one edge of the first electrode 401 and over atleast one of the plurality of sides 406˜110 having the first electrode401 extending thereover.

As can be seen in FIG. 4A, the second electrode 403 does not overlap theentirety of either the first electrode 401 or the piezoelectric layer402. Rather, the second electrode 403 overlaps only a portion of thearea of the first electrode 401 and the piezoelectric layer 402.Moreover, in the representative embodiment depicted in FIG. 4A, thesecond electrode 403 of the FBAR structure 400 does not extend over anyof the plurality of sides 406˜110 of the cavity 404 formed in thesubstrate 405. As such, the active area of the FBAR structure 400, whichis defined as the area of contacting overlap of the second electrode403, the piezoelectric layer 402, the first electrode 401 and the cavity404, is suspended over the cavity 404. As described more fully below, bythis beneficial arrangement, the active area of the FBAR structure 400is substantially mechanically isolated from the substrate 405, andtherefore, is not susceptible to significant mechanical stress from thesubstrate 405. Beneficially, this substantial isolation of the activearea of the FBAR structure 400 from mechanical stress of the substrate405 reduces the drift of the center frequency and bandwidth of the FBARstructure 400.

FIG. 4B is a cross-sectional view of the FBAR structure 400 of FIG. 4Ataken along the line B-B′ of FIG. 4A. The FBAR structure 400 comprisesthe first electrode 401, the piezoelectric layer 402 and the secondelectrode 403 disposed over the cavity 404 in the substrate 405. In thesuspended active area structure of FBAR structure 400, an electricalconnection is made to the second electrode 403 via a bridge 412 thatextends over the piezoelectric layer 402 and the first electrode 401.Illustratively, the bridge 412 is formed according to the teachings ofthe above-referenced, commonly owned U.S. Pat. No. 8,248,825 to Choy, etal. As depicted in FIG. 4B, the bridge 412 is physically separated fromthe piezoelectric layer 402 by space 416, and as such terminates theactive area of the FBAR structure 400. In a representative embodiment,the space 416 is empty, comprising only air. In other representativeembodiments, the space 416 is filled with a non-conductive dielectricmaterial (not shown in FIG. 4B) that provides thermal resistance to thesubstrate 405, which generally comprises silicon.

In a representative embodiment, a passivation layer 414 (not shown inFIG. 4A) is disposed over the second electrode 403. The passivationlayer 414 can be formed of various types of materials, includingaluminum nitride, silicon carbide, BSG, SiO₂, SiN, polysilicon, and thelike. The thickness of the passivation layer 414 should generally besufficient to insulate the layers of FBAR structure 400 from theenvironment, including protection from moisture, corrosives,contaminants, and debris.

As depicted in FIG. 4B, the active area 415 of the FBAR structure 400 issubstantially suspended over the cavity 404. Notably, both the firstelectrode 401 and the piezoelectric layer 402 extend over the side 407.The extension of the piezoelectric layer 402 over side 407 providesmechanical robustness to the FBAR structure 400, and beneficiallyreduces the susceptibility of the FBAR structure 400 to mechanicalfailure or fatigue, especially over time. However, the first electrode401 does not extend over side 406, 408, 409 or 410 of the cavity 404 orover the substrate 405, and the piezoelectric layer 402 is removed orotherwise not formed in region 411. As such, the active area 415 issupported by the first electrode 401 only at side 407 of the cavity 404,and is substantially mechanically isolated from the substrate 405 as aresult.

In the presently described representative embodiment, the active area415 of the FBAR structure 400 is supported through the mechanicalconnection of the first electrode 401 to the substrate 405 over side 407of the cavity 404, and remains unconnected to the remaining sides 406,408, 409 and 410 of the cavity. As such, in the presently describedrepresentative embodiment, the active area 415 is supported through themechanical connection of the first electrode 401 to the substrate 405 ononly one of the plurality of sides 406˜410. As should be appreciated byone of ordinary skill in the art, the fewer the number of sides of thefirst electrode 401 to the substrate 405, the better the mechanicalisolation of the active area 415 from the substrate 405. As such, inrepresentative embodiments, the first electrode 401 is mechanicallyconnected to the substrate 405 through extension of the first electrode401 over at least one of the plurality of sides 406˜410 of the substrate405, but connections to substrate 405 by the extension of firstelectrode 401 over more than two of the plurality of sides 406˜410 isgenerally avoided.

FIG. 5A is top view of an FBAR structure 500 according to arepresentative embodiment. Many details of the FBAR structure 500 aresubstantively the same as those provided in the description of FBARstructures 100˜400. These details are not always repeated in order toavoid obscuring the description of the description of the presentlydescribed representative embodiments.

The FBAR structure 500 comprises a first electrode 501, a piezoelectriclayer 502 (not shown in FIG. SA) and a second electrode 503 stacked overone another. The FBAR structure 500 comprises a cavity 504 formed in asubstrate 505. The cavity comprises a plurality of sides 506˜510, wherein the presently described representative embodiment, the first andsecond electrodes 501, 503 each have one more sides than the pluralityof sides 506˜510. In the present embodiment, the additional side of thefirst and second electrodes 501, 503 allows for the connection of aportion of the first electrode 501 to the second electrode 503, asdescribed below.

In a region 511, the piezoelectric layer 502 is removed or otherwise notformed. As described more fully below, the piezoelectric layer 502 isdisposed over at least a portion of the first electrode 501, and extendsfrom beyond at least one edge of the first electrode 501 and over atleast one of the plurality of sides 506˜110 having the first electrode501 extending thereover.

As can be seen in FIG. 5A, the second electrode 503 does not overlap theentirety of either the first electrode 501 or the piezoelectric layer502. Rather, the second electrode 503 overlaps only a portion of thearea of the first electrode 501 and the piezoelectric layer 502.Moreover, in the representative embodiment depicted in FIG. 5A, thesecond electrode 503 of the FBAR structure 500 does not extend over anyof the plurality of sides 506˜110 of the cavity 504 formed in thesubstrate 505. As such, the active area of the FBAR structure 500, whichis defined as the area of contacting overlap of the second electrode503, the piezoelectric layer 502, the first electrode 501 and the cavity504, is suspended over the cavity 504. As described more fully below, bythis beneficial arrangement, the active area of the FBAR structure 500is substantially mechanically isolated from the substrate 505, andtherefore, is not susceptible to mechanical stress from the substrate505. Beneficially, this substantial isolation of the active area of theFBAR structure 500 from mechanical stress of the substrate 505 reducesthe drift of the center frequency and bandwidth of the FBAR structure500.

FIG. 5B is a cross-sectional view of the FBAR structure 500 of FIG. 5Ataken along the line A-A′ of FIG. 5A. The FBAR structure 500 comprisesthe first electrode 501, the piezoelectric layer 502 and the secondelectrode 503 disposed over the cavity 504 in the substrate 505. In arepresentative embodiment, a passivation layer 514 (not shown in FIG.5A) is disposed over the second electrode 503. The passivation layer 514can be formed of various types of materials, including aluminum nitride,silicon carbide, BSG, SiO₂, SiN, polysilicon, and the like. Thethickness of the passivation layer 514 should generally be sufficient toinsulate the layers of FBAR structure 500 from the environment,including protection from moisture, corrosives, contaminants, anddebris.

As depicted in FIG. 5B, an active area 515 of the FBAR structure 500consists of the contacting overlap of the first electrode 501, thepiezoelectric layer 502, the second electrode 503 and the cavity 504.The active area 515 is substantially suspended over the cavity 504 andis supported by the portion of the first electrode 501 that extends overthe side 506 of the cavity 504 and over the substrate 505. However, thefirst electrode 501 does not extend across side 508 of the cavity 504,and the piezoelectric layer 502 is removed or otherwise not formed inregion 511. As such, the active area 515 is supported at side 506 of thecavity 504, and is substantially mechanically isolated from thesubstrate 505 as a result. Moreover, and in contrast to FBAR structures100˜300 described in connection with representative embodiments above,the piezoelectric layer 502 is removed or otherwise not formed so as tonot extend over the side 506 of the cavity 504 or over the substrate505. Beneficially, by not extending the piezoelectric layer 502 over theside 507 and over the substrate 505, mechanical isolation of the activearea 515 from the mechanical stresses/forces on the substrate 505 isfurther improved.

FIG. 5C is a cross-sectional view of the FBAR structure 500 of FIG. 5Ataken along the line B-B′ of FIG. 5A. The FBAR structure 500 comprisesthe first electrode 501, the piezoelectric layer 502 and the secondelectrode 503 disposed over the cavity 504 in the substrate 105.Notably, a section 516 of the first electrode 501 is removed orotherwise not formed, and creates a break in the first electrode 501along this cross-section for reasons explained below. As depicted inFIG. 5C, the active area 515 of the FBAR structure 500 is substantiallysuspended over the cavity 504 and is supported by the portion of thefirst electrode 501 that extends over the side 507 of the cavity 504.However, the first electrode 501 does not extend across side 510 of thecavity 504, and the piezoelectric layer 502 is removed or otherwise notformed in region 511. As such, the active area 515 is supported at side507 of the cavity 504 by the unconnected portion of first electrode 501,and is substantially mechanically isolated from the substrate 105 as aresult.

As depicted in FIG. 5C, a recess 517 is formed at the overlap of thefirst electrode 501, the second electrode 503 and the passivation layer514. This recess 517 is formed by removing or otherwise not forming thepiezoelectric layer 502 in this portion of the FBAR structure 500. Therecess 517 allows the electrical connection at junction 518 to theportion of the first electrode 501 that extends over the side 507 of thecavity 504 and over the substrate 505.

In the presently described representative embodiment, the active area515 of the FBAR structure 500 is supported through the mechanicalconnection of the first electrode 501 to the substrate 505 over sides506 and 507 of the cavity 504, and remains unconnected to the remainingsides 508, 509 and 510 of the cavity.

As depicted in FIG. 5B, the piezoelectric layer 502 is disposed over atleast a portion of the first electrode 501. However, the piezoelectriclayer 502 is removed or otherwise not formed at a gap 519, extends overthe substrate 505, but terminates at side 507. So, for example, in thepresently described embodiment, the piezoelectric layer 502 is providedover the first electrode 501 and both the first electrode 501 and thepiezoelectric layer 502 extend over the substrate 505, but thepiezoelectric layer 502 terminates at side 507. As such, alongcross-section B-B′ the piezoelectric layer 502 is not continuous due togap 519. Notably, however, providing piezoelectric layer 502 over thesubstrate 505 adjacent to but not extending over side 507 providesmechanical robustness to the FBAR structure 100, and beneficiallyreduces the susceptibility of the FBAR structure 100 to mechanicalfailure or fatigue, especially over time.

FIG. 6A is a top view of an FBAR structure 600 according to arepresentative embodiment. Many details of the FBAR structure 600 aresubstantively the same as those provided in the description of FBARstructures 100˜500. These details are not always repeated in order toavoid obscuring the description of the description of the presentlydescribed representative embodiments.

The FBAR structure 600 comprises a first electrode 601, a piezoelectriclayer (not shown in FIG. 5A) and a second electrode 603 stacked over oneanother. The FBAR structure 600 comprises a cavity 604 formed in asubstrate 605. The cavity comprises a plurality of sides 606˜610, wheregenerally the number of the plurality of sides 606˜610 is the same asthe number of sides of the first and second electrodes 601, 603.

In a region 611, the piezoelectric layer 602 is removed or otherwise notformed. As described more fully below, the piezoelectric layer 602 isdisposed over at least a portion of the first electrode 601, and extendsfrom beyond at least one edge of the first electrode 601 and over atleast one of the plurality of sides 606˜610 having the first electrode601 extending thereover.

As can be seen in FIG. 6A, the second electrode 603 does not overlap theentirety of either the first electrode 601 or the piezoelectric layer602. Rather, the second electrode 603 overlaps only a portion of thearea of the first electrode 601 and the piezoelectric layer 602.Moreover, in the representative embodiment depicted in FIG. 6A, thesecond electrode 603 of the FBAR structure 600 does not extend over anyof the plurality of sides 606˜610 of the cavity 604 formed in thesubstrate 605. As such, the active area of the FBAR structure 600, whichis defined as the area of contacting overlap of the second electrode603, the piezoelectric layer 602, the first electrode 601 and the cavity604, is suspended over the cavity 604. As described more fully below, bythis beneficial arrangement, the active area of the FBAR structure 600is substantially mechanically isolated from the substrate 605, andtherefore, is not susceptible to mechanical stress from the substrate605. Beneficially, this substantial isolation of the active area of theFBAR structure 600 from mechanical stress of the substrate 605 reducesthe drift of the center frequency and bandwidth of the FBAR structure600.

FIG. 6B is a cross-sectional view of the FBAR structure 600 of FIG. 5Ataken along the line A-A′ of FIG. 6A. The FBAR structure 600 comprisesthe first electrode 601, the piezoelectric layer 602 and the secondelectrode 603 disposed over the cavity 604 in the substrate 605. In arepresentative embodiment, a passivation layer 614 (not shown in FIG.5A) is disposed over the second electrode 603. The passivation layer 614can be formed of various types of materials, including aluminum nitride,silicon carbide, BSG, Si_(O2), SiN, polysilicon, and the like. Thethickness of the passivation layer 614 should generally be sufficient toinsulate the layers of FBAR structure 600 from the environment,including protection from moisture, corrosives, contaminants, anddebris.

As depicted in FIG. 6B, an active area 615 of the FBAR structure 500consists of the contacting overlap of the first electrode 601, thepiezoelectric layer 602, the second electrode 603 and the cavity 604.The active area 615 is substantially suspended over the cavity 604 andis supported by the portion of the first electrode 601 that extends overthe side 606 of the cavity 604 and over the substrate 605. However, thefirst electrode 601 does not extend across side 608 of the cavity 604,and the piezoelectric layer 602 is removed or otherwise not formed inregion 611. As such, the active area 615 is supported at side 606 of thecavity 604, and is substantially mechanically isolated from thesubstrate 605 as a result. Moreover, and in contrast to FBAR structures100˜300 described in connection with representative embodiments above,the piezoelectric layer 602 is removed or otherwise not formed so as tonot extend over the side 606 of the cavity 604 or over the substrate605. Beneficially, by not extending the piezoelectric layer 602 over theside 607 and over the substrate 605, mechanical isolation of the activearea 615 from the mechanical stresses/forces on the substrate 605 isfurther improved.

FIG. 6C is a cross-sectional view of the FBAR structure 600 of FIG. 6Ataken along the line B-B′ of FIG. 6A. The FBAR structure 600 comprisesthe first electrode 601, the piezoelectric layer 602 and the secondelectrode 603 disposed over the cavity 604 in the substrate 605.Notably, the first electrode 601 is terminated over the cavity 604 asshown, leaving a section 616 between the first electrode 601 and thesecond electrode 603 for reasons explained below. As depicted in FIG.6C, the active area 615 of the FBAR structure 600 is substantiallysuspended over the cavity 604 and is supported by the portion of thefirst electrode 601 that extends over the side 607 of the cavity 604.However, the first electrode 601 does not extend across side 610 of thecavity 604.

As depicted in FIG. 6C, a recess 617 is formed at the overlap of thefirst electrode 601, the second electrode 603 and the passivation layer614. This recess 617 is formed by removing or otherwise not forming thepiezoelectric layer 602 in this portion of the FBAR structure 500.Through the arrangement of the second electrode 603 at the recess 617the second electrode 603 extends over a portion of the piezoelectriclayer 602 that extends over the side 607 of the cavity 604 and over thesubstrate 605 as shown. By this arrangement, the active area 615 of theFBAR 600 is supported through the mechanical connection of the secondelectrode 603 to the substrate 605 over side 607 of the cavity 604.

In the presently described representative embodiment, the active area615 of the FBAR structure 600 is supported through the mechanicalconnection of the first electrode 601 to the substrate 605 over side 606and through the mechanical connection of the second electrode 603 to theportion of the piezoelectric layer 602 that extends over side 607 of thecavity 604. Moreover, neither the first electrode 601 nor the secondelectrode 603 are formed over remaining sides 608, 609 and 610 of thecavity 604.

As depicted in FIG. 6B, the piezoelectric layer 602 is disposed over atleast a portion of the first electrode 601. However, the piezoelectriclayer 602 is removed or otherwise not formed in the recess 617, butextends over the side 607 and the substrate 605. So, along cross-sectionB-B′ for example, in the presently described embodiment, thepiezoelectric layer 602 is provided over the first electrode 601 andboth the second electrode 603 and the piezoelectric layer 602 extendover the substrate 605 at side 607. As such, along cross-section B-B′the piezoelectric layer 602 is not continuous due to recess 617.Notably, however, providing piezoelectric layer 602 over the substrate605 adjacent to and extending over side 607 provides mechanicalrobustness to the FBAR structure 600. Moreover, an improvement in stressrelief is realized because the active area 615 of the FBAR structure issuspended by comparatively fewer layers thereby leading to bettermechanical isolation from substrate stress passed through the otherlayers.

FIG. 7A is top view of an FBAR structure 700 according to arepresentative embodiment. Many details of the FBAR structure 700 aresubstantively the same as those provided in the description of FBARstructures 100˜600. These details are not always repeated in order toavoid obscuring the description of the presently describedrepresentative embodiments.

The FBAR structure 700 comprises a first electrode 701, a piezoelectriclayer 702 and a second electrode 703 stacked over one another. It isnoted that for convenience of explanation, the piezoelectric layer 702is depicted in FIG. 7A as being transparent so that certain features ofthe first electrode 701 can be described. The piezoelectric layer 702 isnot transparent. Moreover, an optional passivation layer, which isdescribed below, may be provided over the uppermost layers of the FBARstructure 700, and is not shown in FIG. 7A to better present thedescription of the arrangement of the layers of the FBAR structure 700.

The FBAR structure 700 comprises a cavity 704 formed in a substrate 705.The cavity comprises a plurality of sides 706˜710, where generally thenumber of the plurality of sides 706˜710 is the same as the number ofsides of the first and second electrodes 701, 703.

In a region 711, the piezoelectric layer 702 is removed or otherwise notformed. As described more fully below, piezoelectric layer 702 isdisposed over at least a portion of the first electrode 701, and extendsfrom beyond at least one edge of the first electrode 701 and over atleast one of the plurality of sides 706˜710 having the first electrode701 extending thereover.

As can be seen in FIG. 7A, the second electrode 703 does not overlap theentirety of either the first electrode 701 or the piezoelectric layer702. Rather, the second electrode 703 overlaps only a portion of thearea of the first electrode 701 and the piezoelectric layer 702.Moreover, in the representative embodiment depicted in FIG. 7A, thesecond electrode 703 of the FBAR structure 700 does not extend over anyof the plurality of sides 706˜710 of the cavity 704 formed in thesubstrate 705. As such, the active area of the FBAR structure 700, whichis defined as the area of contacting overlap of the second electrode703, the piezoelectric layer 702, the first electrode 701 and the cavity704, is suspended over the cavity 704. By this arrangement, the activearea of the FBAR structure 700 is substantially mechanically isolatedfrom the substrate 705, and therefore, is not susceptible to significantmechanical stress from the substrate 705. Beneficially, this substantialisolation of the active area of the FBAR structure 700 from mechanicalstress of the substrate 705 reduces the drift of the resonant frequencyof the FBAR structure 700.

FIG. 7B is a cross-sectional view of the FBAR structure 700 of FIG. 7Ataken along the line A-A′ of FIG. 7A. The FBAR structure 700 comprisesthe first electrode 701, the piezoelectric layer 702 and the secondelectrode 703 disposed over the cavity 704 in the substrate 705. In arepresentative embodiment, a passivation layer 714 (not shown in FIG.7A) is disposed over the second electrode 703. The passivation layer 714can be formed of various types of materials, including aluminum nitride,silicon carbide, BSG, SiO₂, SiN, polysilicon, and the like. Thethickness of the passivation layer 714 should generally be sufficient toinsulate the layers of FBAR structure 100 from the environment,including protection from moisture, corrosives, contaminants, anddebris.

As depicted in FIG. 7B, an active area 715 of the FBAR structure 700consists of the contacting overlap of the first electrode 701, thepiezoelectric layer 702, the second electrode 703 and the cavity 704.The active area 715 is substantially suspended over the cavity 704 andis supported by the portion of the first electrode 701 and thepiezoelectric layer 702 that extend over the side 706 of the cavity 704.However, the first electrode 701 does not extend across side 709 of thecavity 704, and the piezoelectric layer 702 is removed or otherwise notformed in region 711. As such, the active area 715 is supported at side106 of the cavity 704, and is substantially mechanically isolated fromthe substrate 105 as a result.

FIG. 7C is a cross-sectional view of the FBAR structure 700 of FIG. 7Ataken along the line B-B′ of FIG. 7A. The FBAR structure 700 comprisesthe first electrode 701, the piezoelectric layer 702 and the secondelectrode 703 disposed over the cavity 704 in the substrate 705. In thesuspended active area structure of FBAR structure 700, an electricalconnection is made to the second electrode 703 via a first bridge 716and a second bridge 718 that is separated from the first bridge 716 by arecess 717. As shown, the first bridge 716 and the second bridge 718extend over the piezoelectric layer 702 and the first electrode 701. Thefirst bridge 716 is physically separated from the piezoelectric layer702 by a first space 719, and the second bridge 718 is physicallyseparated from the piezoelectric layer 702 by a second space 720.Notably, the first space 719 terminates the contacting overlap of thefirst electrode 701, the piezoelectric layer 702 and the secondelectrode 703, and as such terminates the active area 715 of the FBARstructure 700. Illustratively, the first and second bridges 716, 718 areformed according to the teachings of the above-referenced, commonlyowned U.S. Pat. No. 8,248,825 to Choy, et al. As depicted in FIG. 7B,the first and second spaces 719, 720, are empty, comprising only air. Inother representative embodiments, the first and second spaces 719, 710are filled with a non-conductive dielectric material (not shown in FIG.7C) that improves the mechanical strength of the bridge and providesthermal resistance to the substrate 705, which generally comprisessilicon.

As depicted in FIG. 7A, the signal feed line (SFL) length iscomparatively larger, and effects improved isolation of the active area715 from the substrate 705. Notably, the implementation of the“double-bridge” arrangement with first bridge 716, recess 717 and secondbridge 718 is done, at least in part, to increase the SFL. As notedabove, the greater the SFL length, the more remote the active area ofthe FBAR structure 100 is from the substrate 105 and the influence ofstress induced on the substrate 105. As such, the length of the bridge112 is made larger compared to known bridges and signal feeds betweenexternal contacts to the FBAR structure. Illustratively, the SFL lengthis at least 25 μm, and typically can be approximately 10 μm toapproximately 100 μm or more. Other structures, such as a double-bridgearrangement described below, can be implemented to provide a suitableSFL length and thus, suitable isolation of the active area of the FBARstructures of representative embodiments.

In a representative embodiment, a passivation layer 714 (not shown inFIG. 4A) is disposed over the second electrode 703. The passivationlayer 714 can be formed of various types of materials, includingaluminum nitride, silicon carbide, BSG, SiO₂, SiN, polysilicon, and thelike. The thickness of the passivation layer 714 should generally besufficient to insulate the layers of FBAR structure 700 from theenvironment, including protection from moisture, corrosives,contaminants, and debris.

As depicted in FIGS. 7B and 7C, the active area 715 of the FBARstructure 700 is substantially suspended over the cavity 704. Notably,both the first electrode 701 and the piezoelectric layer 702 extend overthe sides 707 and 709. The extension of the piezoelectric layer 702 oversides 707, 709 provides mechanical robustness to the FBAR structure 700,and beneficially reduces the susceptibility of the FBAR structure 700 tomechanical failure or fatigue, especially over time. However, the firstelectrode 701 does not extend over the substrate at sides 708 or 710 ofthe cavity 704, and the piezoelectric layer 702 is removed or otherwisenot formed in region 711. As such, the active area 715 is supported bythe first electrode 701 only at two sides 706, 707 of the cavity 704,and is substantially mechanically isolated from the substrate 705 as aresult.

In the presently described representative embodiment, the active area715 of the FBAR structure 700 is supported through the mechanicalconnection of the first electrode 701 to the substrate 705 over sides706, 707 of the cavity 704, and remains unconnected to the remainingsides 708, 709 and 710 of the cavity 704. As such, in the presentlydescribed representative embodiment, the active area 715 is supportedthrough the mechanical connection of the first electrode 701 to thesubstrate 705 on only two of the plurality of sides 706˜710. As shouldbe appreciated by one of ordinary skill in the art, the fewer the numberof sides of the first electrode 701 connected to the substrate 705, thebetter the mechanical isolation of the active area 715 from thesubstrate 705. As such, in representative embodiments, the firstelectrode 701 is mechanically connected to the substrate 705 throughextension of the first electrode 701 over at least one of the pluralityof sides 706˜410 of the substrate 705, but connections to substrate 705by the extension of first electrode 701 over more than two of theplurality of sides 706˜710 are generally avoided.

While representative embodiments are disclosed herein, one of ordinaryskill in the art will appreciate that many variations that are inaccordance with the present teachings are possible and remain within thescope of the appended claims. The invention therefore is not to berestricted except within the scope of the appended claims.

1. A film bulk acoustic resonator (FBAR) structure, comprising: asubstrate comprising a cavity having a plurality of sides; a firstelectrode disposed over the cavity, the first electrode extending overat least one but not all of the sides of the cavity; a piezoelectriclayer disposed over at least a portion of the first electrode, andextending over the at least one of the sides having the first electrodeextending thereover, and a second electrode disposed over thepiezoelectric layer, a contacting overlap of the first electrode, thepiezoelectric layer and the second electrode forming an active area ofthe FBAR.
 2. The FBAR structure of claim 1, wherein the active area issuspended over the cavity and does not extend over any of the sides. 3.The FBAR structure of claim 1, wherein the second electrode extends overonly one of the sides.
 4. The FBAR structure of claim 3, wherein thefirst electrode does not extend over the only one of the sides.
 5. TheFBAR structure of claim 1, further comprising a bridge connecting thesecond electrode to one of the sides.
 6. The FBAR structure of claim 5,wherein a spacer is provided beneath the bridge.
 7. The FBAR structureof claim 6, wherein the spacer is filled with a non-etchableborosilicate glass (NEBSG).
 8. The FBAR structure of claim 7, whereinthe spacer is filled with air.
 9. The FBAR structure of claim 1, whereinthe piezoelectric layer and the first electrode each extend over the atleast one side.
 10. The FBAR structure of claim 9, wherein thepiezoelectric layer and the first electrode each extend over a secondside.
 11. A film bulk acoustic resonator (FBAR) structure, comprising: asubstrate comprising a cavity having a plurality of sides; a firstelectrode disposed over the cavity; a piezoelectric layer disposed overa portion of the first electrode and extending over at least one of thesides; a second electrode disposed over the piezoelectric layer, acontacting overlap of the first electrode, the piezoelectric layer andthe second electrode forming an active area of the FBAR, wherein theactive area of the FBAR is completely suspended over the cavity.
 12. TheFBAR structure of claim 11, further comprising a bridge connecting thesecond electrode to one of the sides.
 13. The FBAR structure of claim11, further comprising a first and a second bridge in disposed in tandemand connecting the second electrode to one of the sides.
 14. The FBARstructure of claim 12, wherein a spacer is provided beneath the bridge.15. The FBAR structure of claim 14, wherein the spacer is filled with anon-etchable borosilicate glass (NEBSG).
 16. The FBAR structure of claim14, wherein the spacer is filled with air.
 17. The FBAR structure ofclaim 11, wherein the first electrode extends over only two of thesides.
 18. The FBAR structure of claim 17, wherein the piezoelectriclayer extends over one of the two sides.
 19. The FBAR structure of claim17, wherein the piezoelectric layer extends over the two sides.